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Put most simply, they constitute a large group of previously free-floating microorganisms that colonise and stick together and then adhere to a surface. To view them simply as a bacterial slime layers is to underestimate them as, in a group, they change their behaviour to act as one body, or biological system. They organise themselves into a co-ordinated functional community, sharing nutrients and protecting themselves from harmful factors within their environment. An example of a biofilm very close to home is tooth plaque. Biofilms, like plaque, can corrode the surface they colonise, so just as we care for our teeth, care needs to be taken in the biofilm control and biofilm removal to ensure the preservation of areas colonised in the wider environment.
Biofilms can be made up of one type of microorganism, or a mixture – of bacteria, fungi and algae, for example, and they are usually found on solid surfaces in contact with liquid. In the built environment biofilm formation occurs very easily in moist warm conditions, particularly if the water with which the film has contact is still or stagnant. Showerheads are a good example; pipework is another. In heating and hot water systems corrosion is a real concern as the lifespan of HVAC systems can be seriously compromised if biofilms form. In addition to this, the build up of biofilm on pipe and heat exchanger surfaces reduces efficiency and restricts flow, particularly in the small-bore pipework work used in most modern buildings. Research has shown that the presence of biofilms also reduces heat transfer.
One of the most common forms of bacteria found in biofilms in HVAC systems throughout the UK is Pseudomonas. Pseudomonas is a family of bacteria widely found in soil and water and although it’s not usually harmful to humans, it can cause lung infections in the weak and vulnerable. More serious is the damage it can do to HVAC equipment through corrosion, attracting Sulphate Reducing Bacteria (SRBs) which are particularly destructive. SRBs metabolise the sulphates in the water to produce sulphides which collect under the biofilm layer. These suphides depolarize the metal surface causing localised pitting, corrosion and eventual perforation.
In order to prevent a build-up of Pseudomonas, care must be taken from the very start – in the design of water systems. For example, features such as dead legs and capped pipes, often added to allow for expansion of the water system at a later date, create the ideal stagnant conditions for the growth of biofilm.
Once the system is in-situ, pre-commissioning cleaning, in-line with BSRIA guidelines is essential, as is ongoing maintenance. In the fight for biofilm removal, it is really important that after-care is well planned and fit for purpose.
One of the key ways to prevent biofilm is to stop the ingress of oxygen. Like all living things, most bacteria need oxygen to thrive. We use condition monitoring solution, Hevasure, to check for Dissolved Oxygen, as well as other parameters such as corrosion rates and pressure levels. This allows potentially adverse water conditions to be nipped in the bud before issues like biofilm are able to develop.
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